Field of Invention
The present invention relates to a field of processing distribution network single-phase-to-earth faults, and more particularly to single-phase-to-earth fault processing device and method for a neutral non-effectively grounded distribution network.
Description of Related Arts
Nowadays the distribution networks in most areas of China adopt the neutral ungrounded operation manner. When the system has a relatively large capacitive current and fails to quench the ground arc, it is necessary to arrange the arc suppression coil. The arc suppression coil is able to obviously increase the power supply reliability of the distribution network, and relatively effectively suppress the intermittent arc ground overvoltage. However, the arc suppression coil is found to have the following problems in usage.
(1) Because of the diversified operation manners of the distribution network and the randomness of the arc ground point, it is difficult for the arc suppression coil to effectively compensate the capacitive current. Moreover, the arc suppression coil merely compensates the power-frequency capacitive current, while in fact, the currents passing the ground point include not only the power-frequency capacitive current, but also a large number of the high-frequency currents and the resistive currents. In worse cases, merely the high-frequency currents and the resistive currents are already enough to sustain the continuous combustion of the arc. Thus, the arc suppression coil fails to completely quench the arc.
(2) When the non-ground fault of the distribution network occurs, such as the break line, the open-phase fault, and the capacitive coupling of the lines on the same tower, the asymmetrical voltage of the distribution network increases, which may cause the automatic adjustment controller of the arc suppression coil to act upon a mistaken judgment that the distribution network is grounded. Herein, a quite high neutral displacement voltage is generated in the distribution network, leading to a great increase in the single-phase voltage or the two-phase voltage in the system and the damages brought to other devices in the distribution network.
(3) The arc suppression coil is set according to specific parameter changes of the distribution network. Thus, with the expansion of the distribution network, the parameter requirements on the arc suppression coil also change, and thus, it is necessary to continuously change the arc suppression coil, which is disadvantageous for the long-range plan and the maintenance management of the distribution network.
Moreover, the fault line selection and the fault section location for the single-phase-to-earth fault of the neutral non-effectively grounded distribution network are always the difficulties in the field of distribution network operation control. Even though no arc suppression coil is arranged, the characteristics of the steady-state zero-sequence current are unobvious. The arc suppression coil compensates the capacitive current of the system by the inductive current of the arc suppression coil, leading to the further decrease of the small capacitive current on the fault line and the more difficult fault line selection and location.